1. Field of the Invention
The present invention relates to methods and apparatus for handling copy sheets in xerographic copiers and the like. More particularly, the present invention relates to methods and apparatus for handling copy sheets through image transferring stations in xerographic copiers or the like. The present invention is especially useful for copier configurations wherein copy paper is curved as it is driven through a latent image transfer station to an output driving means.
2. Description of the Prior Art
Development of compact, low-cost xerographic copiers suitable for use as table-top machines demands substantial efforts toward minimization of the machine volume. Furthermore, design and use of such compact copiers is simplified if the transfer sheet paper path is arranged such that one end or the other of each copy sheet is physically available for extraction from the machine in the event of a jam thereby reducing the necessity for special mechanisms and user procedures to allow internal access to the machine. Such a paper path preferably follows a U-shaped arrangement to avoid interference with other elements associated with the copier. This is particularly true in configurations wherein semiautomatic document feeds or recirculating automatic document feeds are employed.
One example of a highly compact xerographic copier is shown in copending application Ser. No. 173,590 filed July 30, 1980 and entitled "Noncircular Photoconductor Belt Mounting Apparatus and Method" by D. L. Janeway and P. A. Stevenson which is commonly assigned and now issued as U.S. Pat. No. 4,319,829. In this cross-referenced structure, the copy sheets are produced or extracted from a cassette and urged by thrust rollers into a U-shaped paper path including a corona transfer station and thence through fuser rollers before exit to an output pocket on the top of the supply cassette. So long as the rollers associated with the input and the output paths relative to the transfer station are maintained in relatively close parallel alignment, image transfer is generally satisfactory. However, wear of the roller surfaces or any slight misalignment causes copy sheet rotation and skewing so that image blurring occurs when the copy sheet is gripped by the output rollers at the same time that it is propelled by the input rollers. This blurring results from skew of the paper as it passes through the image station and enters the nip of the output rollers. That is, failure of the copy sheet to enter the output roller nip in a true or square relation results in application of skewed forces to the paper which is transferred to the paper at the image transfer station such that the image sometimes tends to blur.
The prior art devices do not resolve the aforementioned copy sheet skewing problem. For instance, the IBM Technical Disclosure Bulletin of June 1980 (Vol. 23, No. 1) at page 71 in the article entitled "Fuser Entry Guide and Paper Bubble Former" by D. C. Estabrooks and C. W. Knappenberger shows a pivotable guide to help accommodate the bubble formed in the copy sheet as it leaves the detack finger downstream from the image transfer station. This bubble is intended to act as a buffer between the differing speeds of the transfer drum and hot roll fuser rollers. It does not properly align the copy sheet leading edge as it enters the fuser nip.
It is also known to employ sloped transition surfaces between pairs of drive rollers for bursting continuous forms wherein the sloped surface and rollers are positioned such that the output rollers squarely receive the copy sheets. This is shown as the curved guide member between first and second feeding roller pairs in the sheet handling apparatus of U.S. Pat. Nos. 3,994,487 by H. P. Wicklund and 4,091,978 by J. E. Graham. Both the Wicklund and Graham devices employ the sloped guide member for the purpose of creating edge stress on continuous web output sheets so that severence of perforations transverse to the sheet commences at the stressed edge and tear or "burst" progressively across the sheet.
Despite the presence of the foregoing prior art, no solution to the copy sheet skewing and image transfer blurring problem associated with passing xerographic copy sheets through transfer stations has evolved as is now available through the present invention.